Decades of chromatography research done with DryLab®.

Chromatographia · 2008

LC Determination of Lercanidipine and Its Impurities Using Drylab Software and Experimental Design Procedures

Igor Popovic, Darko Ivanovic, Mirjana Medenica, Andjelija Malenovic, Biljana Jancic-Stojanovic

The main objective in all optimization procedures is to define the most appropriate conditions for rapid, sensitive, precise, and reproducible analysis, as economically as possible. Experimental design and DryLab optimization software have been used to optimize a liquid chromatographic method for separation of lercanidipine and its three impurities. In both methods of optimization the acetonitrile content and pH of the mobile phase were factors extracted for analysis; resolution of a critical pair was output in both cases. Data obtained from both optimization methods were compared and appropriate conclusions were extracted with the objective of gaining a complete view of chromatographic behavior. Detailed description was obtained by use of a three-dimensional graph and DryLab maps. Both methods of optimization reported the most appropriate mobile phase to be a 35:65 mixture of acetonitrile and an aqueous solution of 1.5% TEA, pH adjusted to 3.0 by addition of orthophosphoric acid, at a flow rate 1.0 mL min−1. Separations were performed on a 20 × 4.6 mm, 3.5-μm particle size, C18 column, at 20 °C, with UV detection at 240 nm. The method was validated. All the results proved the reliability of the method, so it can be used for separation, identification, and simultaneous determination of these substances in the drug and in pharmaceutical dosage forms.

American Chemical Society, Middle Atlantic Regional Meeting, Proceedings, 261 · 2008

Computerized Design of Robust Gradient HPLC Methods

Imre Molnár, Hans-Jürgen Rieger

American Chemical Society · 2008

A Stepwise Strategy for Developing a Robust HPLC Separation for a Novel Diabetes Compound

Frank Hu, Frank Tomasella, Merill Davies

John Wiley · 2007

High-performance gradient elution: the practical application of the linear-solvent-strength model

Lloyd R. Snyder, John W. Dolan

Journal of Chromatography A · 2006

Application of a column selection system and DryLab software for high-performance liquid chromatography method development

Ryan M. Krisko, Kieran McLaughlin, Michael J. Koenigbauer, Craig E. Lunte

This paper describes a strategy for the development of chromatographic methods for drug candidates based upon the use of simple MS compatible mobile phases and optimization of the chromatographic selectivity through variations of the stationary phase and mobile phase pH. The strategy employs an automated column selection system and a series of HPLC columns, varying in hydrophobicity and silanol activity, in combination with DryLab software to develop chromatographic methods for the separation of mixtures of bupivacaine and its metabolites; acidic, basic, and neutral compounds; and atenolol, nitrendipine, and their degradation products.

HPLC 2006 · 2006

Fundamentals of Reversed Phase Chromatography: Solvophobic Theory Redux

Anant Vailaya

Journal of Chromatography A · 2006

Retention modelling in ternary solvent-strength gradient elution reversed-phase chromatography using 30mm columns

Melvin R. Euerby, Federico Scannapieco, Hans-Jürgen Rieger, Imre Molnár

An optimization strategy for ternary solvent-strength gradient elution RP chromatography is described in which a two-dimensional model of gradient time (2 levels) against ternary proportions of organic modifiers (4 levels) was constructed. From the resolution surface the optimum ratio of organic modifiers could be selected. Excellent retention time and acceptable peak width and resolution simulations were obtained. The separation could be further optimized from the same input data by using a standard one-dimensional model in order to optimize for gradient slope, duration and shape. Excellent retention time and acceptable peak width and resolution simulations were obtained (<1, 2 and 6% error, respectively).

Chromatographia · 2005

Searching for Robust HPLC Methods – Csaba Horváth and the Solvophobic Theory

Imre Molnár

This paper is written in remembrance of the work of Csaba Horváth on Reversed Phase Chromatography, (RPC) and the fundamental theory of the mechanism of retention on non-polar stationary phases, the ``Solvophobic Theory''. The paper discusses some steps in the development of this important theory and examines its consequences in developing robust methods for routine RPC. Reliable product quality requires the understanding of selectivity changes, which in RPC govern the development of robust and reliable methods involving continuous changes of liquid chromatographic parameters in aqueous eluents. The application of RPC is still growing in scientific research and in pharmaceutical and chemical production. The impact of the Solvophobic Theory in life sciences has been enormous but it was only a part of Horváth's scientific work. RPC is today one of the most popular, most widely used tools in analytical chemistry and will remain so for many years due to its stability and to its robustness.

Journal of Chromatography A · 2005

A practical approach to transferring linear gradient elution methods

Adam P. Schellinger, Peter W. Carr

Attempts to theoretically address the problems involved in transferring linear gradient elution methods have been somewhat ad hoc due to the simplifying assumptions usually made in conventional gradient elution theory. Until now, all equations based on the k* parameter of linear gradient elution theory used as the basis for predicting the separation selectivity have not explicitly included the effect of the dwell volume (VD). Using an exact equation for predicting k*, that is, one which fully accounts in an a priori fashion for VD, we find a set of simple yet exact equations which unequivocally must be satisfied to transfer an optimized linear gradient elution method from one system (column or instrument or both) to another. These relationships absolutely mandate that a change in the instrument dwell volume requires a proportional change in the column volume; in turn, a change in the column volume requires a proportional change in the flow rate and/or gradient time to maintain a constant gradient steepness. Although we are not the first to suggest these guidelines, this work provides a complete theoretical foundation for these exact guidelines for the maintenance of gradient selectivity for the case of transferring a linear gradient elution method between different columns packed with the same particles and/or between different instruments.

Electrophoresis · 2004

Microemulsion electrokinetic chromatography of drugs varying in charge and hydrophobicity Part II: Strategies for optimization of separation

Valérie Harang, Sven P. Jacobsson, Douglas Westerlund

The separation of anionic, cationic, and neutral drugs in microemulsion electrokinetic chromatography (MEEKC) was studied. The concentration of sodium dodecyl sulfate (SDS; surfactant) and 2-propanol (organic solvent) was varied in a three-level full factorial design. 29 different model substances were chosen with different hydrophobicities and charges (neutral, positive, and negative). The models were calculated by means of multiple linear regression (MLR). The compounds were divided into five different subgroups, and different strategies for optimization of the separation within each group were investigated. The optimization was done by maximizing the selectivity using response surface plots in MODDE, by calculation of different chromatographic functions, and by using the software DryLab. For all the different groups, MODDE, almost all chromatographic functions and DryLab gave approximately the same settings of the factors for optimum separation. Attempts were made to fit descriptors of the compounds to the retention data from the three-level full factorial design by means of partial least squares projection to latent structures (PLS). Between 86 and 89% of all predictions of migration times were acceptable (80-120% of the observed value).

Journal of Chromatography A · 2003

Computer-assisted method development and optimization in high-performance liquid chromatography

T. H. Hoang, D. Cuerrier, S. McClintock, M. Di Maso

This paper reports the use of DryLab, a computer simulation software package, to assist in the development and optimization of a reversed-phase high-performance liquid chromatographic (HPLC) method for the separation of a model drug candidate and its degradation products. Prior to the optimization process, columns with various bonded phases are evaluated for their chromatographic performance using the sample of interest. Simultaneous optimization of two separation variables and the use of resolution maps to predict the optimal conditions are illustrated. Options to optimize column conditions (column length and flow-rate) to further reduce run time are briefly discussed. The accuracy of DryLab-predicted retention times and resolution is compared with experimental values. The DryLab software used in this study provided satisfactory predictions for the selected model, with average errors of less than 3.5 and 11.8% for retention time and resolution, respectively.

LC GC Europe · 2002

Optimizing Multilinear Gradients in HPLC

Tom H. Jupille, Lloyd R. Snyder, Imre Molnár

Multilinear gradients have not been widely used in general purpose high performance liquid chromatography, in part because of experimental inconvenience in method development. Even with the use of computer modelling, identifying an optimum set of breakpoints has primarily been done by trial and error. Combining a spreadsheet with controllable chromatography modelling software has allowed us to implement a systematic approach to bi- and tri-linear gradient optimization. Application of this approach to 10 randomly generated sample sets suggests that the improvement in critical resolution that can be obtained is considerably smaller than that obtained through the use of a second selectivity variable. Because no additional experimental time (and only limited computational time) is required once an optimum linear gradient has been modelled, however, any improvement thus gained is essentially "free".

Journal of Chromatography A · 2002

Lipophilicity and pKa estimates from gradient high-performance liquid chromatography

Roman Kaliszan, Piotr Haber, Tomasz Bączek, Danuta Siluk, Klara Valko

The linear-solvent strength (LSS) model of gradient elution has been applied to estimate parameters of lipophilicity and acidity of a series of drugs and model chemicals. Apparent pKa values and log kw values for individual analytes were determined in 2–3 gradient runs. The first experiment (or first two experiments) uses a wide-range organic modifier gradient with pH chosen for suppressed ionization of the analyte. The result of this experiment allows an estimate of contents of organic modifier of the mobile phase (%B) providing the required retention coefficient, k, for the non-ionized analyte. The following experiment is carried out with the latter %B and a pH-gradient of the aqueous component of the eluent that is sufficient to overlap the possible pKa-value of the analyte. The initial pH of the buffer used to make the mobile phase is selected to insure that the analyte is in non-ionized form. The resulting retention time allows an estimate of pKa in a solvent of the selected %B. At the same time, estimates of log kw can also be obtained. The log kw parameter obtained from gradient HPLC by the approach proposed correlated well with the corresponding value obtained by standard procedure of extrapolation of retention data determined in a series of isocratic measurements. Correlation between log kw and the reference parameter of lipophilicity, log P, was very good for a series of test analytes and satisfactory for a structurally diverse series of drugs. The approach supported with specific detection procedures can be recommended for fast screening of lipophilicity of individual components of complex mixtures like those produced by combinatorial chemistry. The values of pKa obtained in a study were found to correlate with the literature pKa data determined in water for a set of aniline derivatives studied. In case of a series of drugs the correlation was less than moderate if the general procedure of pKa determination was applied.

Journal of Chromatography A · 2002

Advanced high-performance liquid chromatography method development: Discovering unexpected choices in chromatography

Imre Molnár, Hans-Jürgen Rieger

The influence of some important experimental parameters on the resolution of compounds as well as the validity of widely used rules of thumb and of common expectations about how to improve resolution is discussed. It will be shown, on the basis of selected examples, that the general expectations about how the experimental parameters have to be adjusted for better resolution does not cover all chances for resolution improvement. The tool for understanding the method and to discover all chances for increasing selectivity is the resolution map of a method.

Journal of Chromatography A · 2002

Variability of column selectivity for reversed-phase high-performance liquid chromatography: Compensation by adjustment of separation conditions

J. W Dolan, L. R Snyder, T. H Jupille, N. S Wilson

Reversed-phase columns are widely used in assays based on high-performance liquid chromatography (HPLC). When such assays are repeated over time, it is often necessary to replace the column. In such cases, the selectivity of columns from different production batches may prove sufficiently variable to result in a failed separation. It is possible to compensate for differences in column selectivity by making small changes (adjustments) in separation conditions. The present paper describes an efficient procedure for choosing adjusted conditions and discusses its general applicability.

Journal of Chromatography A · 2002

Two-dimensional optimization using different pairs of variables for the reversed-phase high-performance liquid chromatographic separation of a mixture of acidic compounds

Tom H. Jupille, John W. Dolan, Lloyd R. Snyder, Imre Molnár

Computer-facilitated method development has been extended for the simultaneous optimization of any two variables in separations by HPLC and other chromatographic procedures (gas chromatography, supercritical fluid chromatography, capillary electrophoresis, etc.). The application of this approach to HPLC method development is illustrated by the reversed-phase separation of a nine-component mixture of organic acids. Two of four variables (temperature, solvent strength (%B), pH and buffer concentration) were separately optimized in terms of selectivity, and the results are compared in terms of which variables and other conditions are most effective in providing maximum resolution for samples that contain ionizable compounds.

Acta Chromatographica · 2002

Computer Optimization of the RP-HPLC Separation of Some Taxoids from Yew Extracts

M. Ł Hajnos, M. Waksmundzka-Hajnos, K. Głowniak

Drylab G software has been used to optimize the reversed-phase HPLC separation of taxoids and co-extracted substances from yew. Two preliminary runs based on a linear gradient from 5 to 100% acetonitrile (ACN) in 20 or 60 min were shown to be satisfactory for optimization of resolution. The optimization experiments were performed on a purified extract fortified with taxoid standards. The identity and purity of the peaks were verified by use of photodiode-array detection. Agreement between simulated and experimental data was good. The optimized chromatographic system can be used for quantitative analysis of paclitaxel, cephalomannine, and 10-deacetylbaccatin in yew extracts.

Analytical and Bioanalytical Chemistry · 2002

Use of DRYLAB to compare octadecylsilane and carbon supports for reversed-phase chromatography of triazine herbicide test solutes

Adam P. Schellinger, Yun Mao, Peter W. Carr

One of the most important aspects of method development in reversed-phase high-performance liquid chromatography (RPLC) is the accurate prediction of the resolution as one or more experimental variables (usually the mobile-phase composition) are changed. By use of commercially available computer simulation programs, e.g. Drylab 2000, data from a few initial experimental runs are used to predict how the separation will vary with composition so that a computer program can then rapidly locate the optimum conditions. Assumption of a linear relationship between log k′ (retention factor) and φ (volume fraction of organic modifier in the element) minimizes the number of initial runs required for a separation and is usually adequate when the range of φ is not large. In this work the linearity of plots of log k′ against φ for octadecylsilane-coated silica (ODS) and carbon-coated zirconia (C-ZrO2) columns were compared and the plots were used to determine whether prediction of the separation of triazine herbicides was adequate. Analysis of the slopes and intercepts of such plots are presented for both types of columns.

Journal of Chromatography A · 2002

Computerized design of separation strategies by reversed-phase liquid chromatography: development of DryLab software

Imre Molnár

The development of DryLab software is a special achievement in analytical HPLC which took place in the last 16 years. This paper tries to collect some of the historical mile stones and concepts. DryLab, being always subject to change according to the needs of the user, never stopped being developed. Under the influence of an ever changing science market, the DryLab development team had to consider not just scientific improvements, but also new technological achievements, such as the introduction of Windows 1.0 and 3.1, and later Windows NT and 2000. The recent availability of new 32-bit programming tools allowed calculations of chromatograms to be completed more quickly so as to show peak movements which result for example from slight changes in eluent pH. DryLab is a great success of interdisciplinary and intercontinental cooperation by many scientists.

LC-GC Europe · 2001

Computer-Assisted Optimization of Reversed-Phase HPLC Isocratic Separations of Neutral Compounds

Tomasz Baczek, Roman Kaliszan, H.A. Claessens, M.A. Straten

Rational selection of optimized experimental conditions for chromatographic separation of analytes is realized nowadays by means of specialized computer programs. Two such programs, DryLab (LC Resources, Walnut Creek, California, USA) and ChromSword (Merck KCaA, Darmstadt, Germany), were compared in this research. The aim of the study was to compare the optimization of chromatographic separations of neutral compounds performed isocratically in reversed-phase high performance liquid chromatography (HPLC) systems. A detailed description and discussion of the differences in predicted and experimental chromatographic retention parameters is reported. The conclusion reached is that the two programs provide identical predictions of retention data, when predictions are based on two initial experimental chromatographic measurements. An additional option of ChromSword, employing the quantitative structure-retention relationships (QSRR), appears to provide satisfactory predictions of the separation when molecular structural data along with retention data from a single initial experimental run are used as inputs. Predictions based on molecular structure alone are not very accurate and are not likely to provide useful separation information.